AIM: Most young people fail to receive professional treatment for mental disorders; however, they do indicate a preference for sharing problems with peers. This article describes key messages about knowledge and actions to form the basis of a basic mental health first aid (MHFA) course for adolescents to increase recognition of and help seeking for mental health problems by teaching the best knowledge and helping actions a young person can undertake to support a peer with a mental health problem. METHODS: The Delphi method was used to achieve consensus among Australian and Canadian youth mental health experts regarding the importance of statements that describe helping actions a young person can take, and information they should have, to support a friend with a mental health problem. There were two expert panels, one consisting of 36 youth mental health consumer advocates and the other of 97 Youth MHFA instructors. Panellists rated each statement according to how appropriate it would be as a basic mental health first aid message for both a junior adolescent (12-15 years) and a senior adolescent (16-18 years). RESULTS: Out of 98 statements, 78 were endorsed as key basic MHFA messages for junior adolescents and 81 were endorsed for senior adolescents. CONCLUSION: The study has identified key messages for adolescents on how they can help a peer. These messages will form the basis of the curriculum for an MHFA course for adolescents, which will aim to facilitate early recognition of and help seeking for mental health problems in adolescents.